The present invention pertains to surface acoustic wave devices and more particularly to low insertion loss surface acoustic wave devices.
Surface acoustic wave (SAW) devices are typically small filtering elements used in RF applications. Mounting of the SAW on a substrate and electrical interconnection of input and outputs to the SAW device introduce parasitic capacitance and resistance which result in relatively high insertion loss and increased RF feedthrough. Typical SAW devices exhibit RF feedthrough which results in severe distortions in the frequency response causing spurious signals to be induced in the output signals. The spurious signals occur as the result of capacitive and resistive coupling between the closely spaced interface circuits and the SAW device.
Typical solutions to this problem have been to separate the SAW device sufficiently from the external circuitry to reduce the capacitive coupling to a negligible levels. However, for surface mount applications, the overall package size must be minimized. Thus, the SAW device must be fabricated to be as small as possible and in situations in which multiple SAW transducers are used, they must be packaged in physically close proximity. In this situation, increased. Also, spurious electrical currents are induced in the substrate material to which the SAW devices are bonded.
Therefore, it would be highly desirable to produce a relatively small sized SAW package for surface mount applications which is low in insertion loss and direct RF feedthrough.